Like many other viruses in honey bees, DWV spreads in two ways. Worker honey bees (Apis mellifera) will transmit it orally to other workers, generally resulting in a benign infection. But the parasitic varroa mite (Varroa destructor) is a carrier, too. When the mite feeds on bee pupae, infecting them with DWV, the virus causes horrible deformities. Young bees develop with bloated abdomens and shrunken or crumpled wings, making DWV one of the worst viral diseases in commercial honey bee hives. They often die in less than 48 hours.
DWV first turned up in 2004 among commercial bumblebees; the insect, Bombus terrestris, is often used in greenhouses, particularly to pollinate tomatoes. Commercial breeders initially noticed that about 10% of their bumblebee queens had died with tiny, misshapen wings. Then, Elke Genersch of the Institute for Bee Research in Hohen Neuendorf, Germany, and colleagues discovered that the dead bumblebees had been infected with DWV. The researchers suspected that honey bees had orally infected the bumblebees, because breeders use honey bees to encourage bumblebee queens to start new nests.
No one knew the extent of DWV in wild bumblebees. Matthias Fürst and Mark Brown of Royal Holloway, University of London, in Egham and colleagues collected honey bees and bumblebees from 26 sites across Great Britain. The virus was present in 11% of the bumblebees and replicating in more than a third of those, suggesting active infections, they report in Nature.
The team found genetic evidence that the virus is shared between the species: When honey bees and bumblebees lived near each other, both had a similar strain of the virus. Because DWV was more prevalent in honey bees - 36% were infected - the researchers believe it spreads from them to bumblebees. The team also found the same pattern with the fungal pathogen Nosema ceranae, but it did not appear to cause problems for bumblebees.
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